Heretofore in wide use as motor vehicle evaporators are those of the so-called stacked plate type which comprise a plurality of flat hollow bodies arranged in parallel and each composed of a pair of dishlike plates facing toward each other and brazed to each other along peripheral edges thereof, and a louvered corrugated fin disposed between and brazed to each adjacent pair of flat hollow bodies. In recent years, however, it has been demanded to provide evaporators further reduced in size and weight and exhibiting higher performance.
To meet such a demand, the present applicant has already proposed evaporators which comprise a first and a second header tank arranged as spaced apart from each other, and a heat exchange core provided between the two header tanks, each of the two header tanks having a front portion and a rear portion which are symmetric in cross sectional contour, the first header tank having its interior divided by a partition wall with respect to the direction of flow of air through the evaporator into a refrigerant inlet header positioned downstream with respect to the direction of flow of air and a refrigerant outlet header positioned upstream with respect to the direction of flow of air, the outlet header having its interior divided into upper and lower two spaces by a flow dividing resistance plate formed integrally with the outlet header, the resistance plate being provided with a plurality of refrigerant passing holes, the second header tank having its interior divided by a partition wall with respect to the direction of flow of air into a refrigerant inflow header positioned downstream with respect to the direction of flow of air and a refrigerant outflow header positioned upstream with respect to the direction of flow of air, the heat exchange core comprising tube groups in the form of a plurality of rows arranged in the direction of flow of air and each comprising a plurality of heat exchange tubes arranged at a spacing longitudinally of the tanks, the heat exchange tubes of at least one tube group having opposite ends joined respectively to the inlet header and the inflow header, the heat exchange tubes of another tube group having opposite ends joined respectively to the outlet header and the outflow header (see the publication of JP-A No. 2003-75024). The evaporator is fabricated by tacking the components in combination and brazing the tacked assembly collectively.
With this evaporator, the flow dividing resistance plate functions to permit the refrigerant to flow through all the heat exchange tubes of the tube groups in uniform quantities, thereby enabling the evaporator to exhibit improved heat exchange performance.
However, the front and rear portions of the first header tank are symmetric in cross sectional contour, and the flow dividing resistance plate can not be recognized from outside, so that in assembling the components for the fabrication of the evaporator, it is likely that the header tank will be incorporated into the assembly, as oriented longitudinally in the opposite direction. It is then almost impossible to obtain the effect to cause the refrigerant to flow through all the heat exchange tubes in uniform quantities, and there is the likelihood of the evaporator exhibiting greatly impaired refrigeration performance.
Further in order to uniformalize the quantities of refrigerant to be passed through all the heat exchange tubes, it is likely that a plurality of refrigerant passing holes which are different in shape and/or size will be formed in the flow dividing resistance plate asymmetrically longitudinally of the refrigerant outlet header as shown in FIGS. 15 and 16 of the above publication.
However, since the positions of the refrigerant passing holes can not be recognized from outside in assembling the components for the fabrication of the evaporator, the resistance plate is likely to be incorporated as oriented longitudinally in the opposite direction into the assembly. It is then almost impossible to obtain the effect to cause the refrigerant to flow through all the heat exchange tubes in uniformalized quantities, and the evaporator will exhibit seriously impaired refrigeration performance.
An object of the present invention is to overcome the above problems and to provide a heat exchanger which is outstanding in heat exchange performance.